The present invention relates to a carrier injection sensorless position system for use in dynamoelectric machines.
In motor drive applications, information about the position and angular velocity of the rotor is required to optimally control the phase and frequency of power provided to drive the motor. A variety of different types of sensors have been used over the years to resolve the position and angular velocity of the rotor. However, the use of dedicated sensors adds additional size, weight and complexity to the motor.
To reduce the cost associated with dedicated position resolvers, a variety of self-sensing or sensorless systems have been developed that are capable of detecting the position of the rotor. For instance, some systems detect rotor position by monitoring the back electromotive force (BEMF) generated by the dynamoelectric machine. However, at low speeds (i.e., low angular velocities) the monitored BEMF is too small to provide accurate detection of rotor position and speed. In response to this problem, prior art methods stimulate the dynamoelectric machine by injecting a high-frequency carrier signal.
For example, a saliency tracking system works by applying a carrier signal having a frequency greater than the angular velocity of the rotor such that the injected carrier signal sweeps around the machine faster than the rotor is turning. Saliencies within the machine act to vary the impedance of the rotor as seen by the high-frequency carrier signal, and the varied impedance alters the resulting signal (e.g., rotating current waveform or potential waveform). Monitoring and demodulation of the resulting signal allows rotor position and velocity to be determined. However, unbalances in the high-frequency carrier signal injected into the dynamoelectric machine cause modifications to the resulting signal that result in incorrect estimation of the rotor position and velocity.